Fabrication of oriented L1-FePt and FePd nanoparticles with large coercivity

Abstract

Oriented L10-FePt and FePd nanoparticles with coercivities as large as 5 kOe (FePt) and 3 kOe (FePd) were fabricated by alternating deposition of Pt(or Pd) and Fe nanoparticles and their annealing at the temperatures between 773 and 873 K on single crystal NaCl and MgO. Atomic ordering reactions and degrees of order towards the L10-structure formation in these nanoparticles were investigated by high resolution electron microscopy and electron diffraction, and magnetic coercivities at low temperature were also measured. The long range order parameter of the FePt nanoparticles was ∼0.56 even after annealing at 873 K for 24 h. The coercivity of the FePt nanoparticles at 100 K was as high as twice the room temperature value. The low degree of order in the L10-structure formation and the thermal effect on magnetization have been found in the present FePt and FePd nanoparticles. These are closely concerned with the origin of the coercivity values which are very small in comparison with those expected from the single magnetic domain theory.